Miss Marple Series III: Towards Zero

Lady Tressilian hosts a house party where Mary and Treves help to entertain the guests. Miss Marple is interested when Treves tells a story about a child murderer who was never convicted. The next day Treves turns up dead from an apparent heart attack. When Lady Tressilian turns up dead as well, Superintendent Mallard is brought in to investigate. He immediately suspects Audrey, but Miss Marple believes that explanation is too simple and starts an investigation of her own.